1. Field of the Invention
The present invention relates to a technique for adjusting the time for driving a print head according to the characteristics of the print paper. More specifically, the invention relates to a technique for adjusting the time for driving a print head based on different absorptivity of print papers used in an ink-jet printer, so that the amount of ink emerging from the nozzles of the head can be optimally controlled. This results in a high print resolution.
2. Description of the Related Art
As is well known, an ink-jet printer performs a printing job by accelerating and directing ink through nozzles thereof. Responsive to head drive pulses having a 2-3 .mu.s pulse width, the ink-jet printer heats the ink. When heated, the ink generates bubbles in it. The bubbles cause the ink to emerge from the nozzles to form characters on the print paper.
The nozzles are stopped from moving for an extremely small amount of time, so called the head driving time, to enable the nozzles to spray the ink on the paper. The head driving time is designated based on the characteristics of the ink in the cartridge of the printer. A monochrome ink cartridge and a color ink cartridge that are generally used in an ink-jet printer have a unique head driving time for each.
For example, the monochrome ink cartridge has a head driving time of 3.5 .mu.s. The color ink cartridge has a head driving time of approximately 2.5 .mu.s, which is little shorter than the head driving time for the monochrome ink cartridge.
In earlier ink jet printers, a plurality of drive transistors in a head driver respectively drive a plurality of heating elements, each heating element corresponding to one nozzle in the printer head. Power is supplied to a single heating element and as a result, ink is sprayed out of the corresponding nozzle.
The time for driving a head is determined by the width of the head driving pulse. Such a head driving apparatus capable of changing the width of the head driving pulse includes a head driver, a heating portion, and a pulse width changing portion for changing the head driving time.
The pulse width changing portion includes a head driving time setter and a pulse generator. The head driving time setter sets the time for driving the nozzles according to the change in power for driving the head. The pulse generator outputs head driving pulses of uniform width with the time set by the head driving time setter. In addition, a controller is electrically connected to and supplies control signals for changing the width of the head driving pulse to the head driving time setter.
The head driving time determines the amount of ink sprayed from the nozzle to the paper. The absorption of the paper depends on the amount of the sprayed ink, the weight per unit area of the paper, the quality of the paper, and the surface of the paper. Such an absorptivity of the paper affects the print resolution on the paper.
If the amount of ink sprayed does not exceed the absorptivity of the paper, there is no surplus ink that may be sprayed on the paper. On the other hand, if the amount of ink spread on the paper is excessive, with respect to the absorptivity of the paper, surplus ink spreads on the paper and causes a deterioration in the print resolution.
Since the amount of ink sprayed by the head is dependent upon the head driving time, a unique head driving time should be determined based on the consideration of the kind of ink jet printer and the absorptivity of the paper.
However, earlier ink jet printers have a head driving time determined without any consideration of the absorptivity of the paper. In the event that the head driving time is excessive with respect to the characteristics of the paper, an excess amount of the ink is sprayed on the paper, thereby causing a deterioration in the print resolution.
The Miyakawa patent, U.S. Pat. No. 4,617,580, entitled Apparatus For Recording On Different Types Of Mediums, discloses an apparatus which controls the density of the image recorded by the ink jet printing unit in accordance with a determination as to the choice of recording medium.
The Moriyama patent, U.S. Pat. No. 4,847,638, entitled Recorder, discloses a recording apparatus which adjusts the discharge timing of the ink from a print head in accordance with the thickness of the recording medium.
The Noaki patent, U.S. Pat. No. 5,504,506, entitled Information Recording Method Capable Of Performing A High Quality Recording In Accordance With Printing Conditions, discloses an image recording technique which varies the recording in accordance with the recording medium used.
Lastly, the Shibamiya patent, U.S. Pat. No. 5,432,533, entitled Recording Method With Control of Head Energization And Recording Medium Conveyance Power Consumption, discloses a recording technique in which the density is varied in accordance with the resultant image on different recording mediums.
While each of the afore-cited patents disclose features in common with the present invention, none of these patents teaches or suggests adjusting the driving time of the print head according to the characteristics of the recording paper as in the present invention.